I've done the android phone thing many times.  Of course, I have an Android phone so, yea its easy. lol.  Seriously though you can get a burner or even on of those cheap android tablets.  Last time I did the tablet thing and it worked well for paying as well as browsing the site.

I also had fine luck with Vanilla cards in the past but I tried one just a bit ago and it didn't work, which was the second card I tried after a prepaid MC from Target didn't go through either.  A WalMart prepaid Visa card worked last time, but the printed terms (US Only, nothing international) are the same as the Vanilla card I got today.  I see they still have a website to register and give an address, so maybe I will try one of those, but I am also hoping someone else can provide current intel - am I correct to assume the Google Pay method is to setup a burner Android with an account linked to a prepaid card, then use the App to make the purchase through the Google Pay?  I've never used the app, only the website, but I can setup a burner phone easy enough...

Go to an ATM and withdraw what you need in cash. Everything else is more hassle for both of you. If she doesn't want to carry a lot of cash alone, offer to escort her to her bank's ATM where she can deposit it.  

The only reason not to use cash is if she isn't paying tax on any income, but I think that it is a low risk for her, especially if she has a real life job.